Conventionally, in a machine tool or the like, in order to dispose a regenerative energy generated when a servo motor driving a rotational axis of a movable portion thereof is slowed down, a system comprising both a resistance regenerating function of consuming regenerative energy in a regenerative resistor and a power supply regenerating function of regenerating the regenerative energy on an AC power supply side is known (PLT 1).
In contrast, in a industry robot, the regenerative energy generated when a servo motor connected to a rotational axis of a movable portion of a robot arm or the like is slowed down is usually smaller than the regenerative energy generated when a servo motor driving a rotational axis of a movable portion of a machine tool or the like is slowed down. Therefore, when the regenerative energy is expected to increase according to an increase of operation load factor of a robot, reinforcing the resistance regenerating function has been general rather than adding the power supply regenerating function.
However, also in an industrial robot, the regenerative energy generated in a servo motor becomes extremely large when an operation is performed at an extremely high load factor (repeating start/stop frequently), and therefore it is desirable to comprise the power supply regenerating function of regenerating the electric power into the power supply in addition to the resistance regenerating function of consuming the regenerative energy by the regenerative resistor.